Side-chain oxidation



Hallo sTA'rEs PATENT OFFICE.

' VIBGI'L GOBLENTZ AND HAROLD W. OF NEW YORK, N. Y., ASSIGNOBS TO COMMERCIAL RESEARCH COM IANY,- OF NEW YORK, 11'. Y., A CORPORATION OF NEW YORK.

Io Drawing.

4 I COBLENTZ and Be it known'that W8,VIRGIL \V. WALKER, citizens of the United States, VIRGIL Conuas'rzbein New York, inthe county of .L State of New York,' and'H -\norn W. being a vresidentof .NewtYork,'in the county and State of New York, have invented certain new and usefi l'lmproveinents' in Side.- Chain' Oxidation, of which the following is a s ecific'ation.

his invention relates to s de-chain oxidation's'and it comprises a method of oxidizing side-chains oraliphatic-groups carried .b

as the ,CH, group of tolueneto forn1-ac1ds,-wherein the material to be oxid withnitric acid of mode a'lomatic or cyclic-hydrocarbon groups, suc

dizedis stratifi crate strength,"bestaround 40 percent.

HNO,, and allowed to at a rather high-temperaturathe operation being carried out undera refluxcondenser of air or oxygen or other conditions allowing return of. valpors for o'xid's'ot nitrogen;

after set forth and asclaiined. i Toluene, C,H,;.CH .,,"can"be benzoic acid, 'C-,H .,.O,H, by oxidation'with converted into pounds to a greater or less extenh': The usual commercial way of.- making benzoicacid from toluene i's first to convert the toluene into. a chlorinated'derivative and their oxidize this body; The'ofiic'ial requirements, however, for benzoic acid laid down in the various V pharmacopinias require a 'chlorinfree material andit -i'sdiflicult, to producethis bythe. oxidation of chlorinated deriva-- tives of toluene.

acid is readily e In a practical embodiment of our method,

' .we simply stratify toluenelandnitric acid- We hai'efound that, contrary to the usual view, 'nzoic acid can produced in large yield, 'practicallv a theoretical yleld, by di'- rect oxidation 0 sity of preliminarily chlorinating the to luene; -In :so doing, a chlorin-free benzoic produced.

of moderate streng th" getherj' leave a resident of ew York. and

oHz a) r rernain inquiet ophtact. therewitlifor-a relatively long period tricacid, but-'the'yields are-"very. 'poor, 'only a few per gentler-theory. being obtained by-ithe described methods... Strong nitric acid converts toluene into: con

toluene with nitric acid'under regulatedconditions. without the neces-l s ns-client oxmarlom,

Specification of Letters Patent. I Patenfed Feb. 2-1, 1920- Application' llled April], -19 18. Serial No. 285,2. v

them undisturbed-at rather a high temperature for-some time..' .Yorking at a tempera- .ture of about 90 Q'with a nitric acid of '-38 per cent. HNO, undera reflux condenser, completeoxidation usually takes four or tivedays. The reaction is somewhat longer in starting. with. fresh nitric acid, and wlth fresh nitric acid it is advantageous to adda-catalystor body servingto start the evolution of nitrous vapors. Ordinary formaldehyde'solution'. or paraformaldehyde, may .be employed. However, any other material (copper, zinc, starch, etc.) serving toinitiate a reduction of the'nitric acid. will do. But i we-find the use of-solid paraformaldehyde ,be the best, since iftgives a quick initial reduction of the nitric acid starting the re- :action and-it does not contaminate the solu tion. "With return of acid, which has already served for. one operation, for admixture witlrfresh acid, the operation is considerably shortened. The greater the sur iac'e of contact between the overlying tolu ene and the underlying nitric acid, other things being equal, the shorter the period required for oxidation. The oxidation is, at least in large part, dependent on the oxidizing action of yapors'of nitrogen oxids passingupwardinto the layer oftol'uene. "Nitrons vapors. that is vapors of. the various nitrogen ox-ids, may be introduced intothe toluene from another source; that is, instead ofusin-g niric acid, vaporsot these 'oxids may be'used. However, the use ofnitric acid itself in the manner described we consider adesi'rabl'e mode'of operation since'it gives the 'apors. so to speak, in statu 'nasce-ridi. Passing beyond the toluene, the vapors. are reoxidized by the air present and, with, operation under a reflux condenser, the reoxidized' vapors are ret-urned to the reaction zone for service anew. In ordinary operation, considerably more than the calculated oxidizing value can be obtained from a. given amount of nitric acidbecause of thisaerial oxidation of these vapors. Stirring the reaction mixture is inadvisable as interfering with the regularity of opera tion. For one thing, it disturbs the stratification, stirring the two layers into each other; and for another, it causes a tempo- .rary rapid disengagementof oxidizing gases or vapors without opportunity for effective contact with-the toluene. Instead of returnthe condensed vapors by- .a reflux to'flm body of liquids from which they originated,

they of course may be sent into another similar body, as by the use of the. ordinary Woulfe bottle arrangement. The different bodies of material may be out of phase with each other; that is, ages. For example, vapors coming from materials which have been under treatment for a day may be led into a fresh batch.

The layer'of toluene lying above the acid is gradually converted into benzoic acid and finally becomes a solid crust of crystallized crude benzoic acid, usuall containingmore or less toluene and some enzaldehyde. As the action goes on, the specific gravity of the oily layer becomes greater because of the solution of benzoic acid therein but as long as the materials are kept hot, it does not tend to settle. The progress of'the reaction can be ascertained by dip in a cold "lass rod into the oil layer. t t e end 0- the action the oily ayer tends to becomesol'id even while hot. -Any. suitable arrangement may be employed for'maintaining the temperature of the materials. a

A strength of around 40 per cent. of nitric acid is considered best for the resent purposes. For good operation t e practical limits may be considered between 36 per cent. and 43 per cent. As the oxidation goes on, the strength of the acid lessens until at the e 'd it may be as low as.12 per cent.,

although it is more usually 16 to 18 per cent.

'It somewhat accelerates the action to strengthen the underlying acid layer after 1 or 2 days running. A good charge 'for 100 pounds of toluene is about 1- carboy (140 unds, approximately) of nitric acid of 42 aum and 110 pounds of spent acid containing about 12 per cent. nitric acid. With the'use of spent acid containing lower oxids of nitrogen, organic matter, etc., no startin catalyst is necessary, although it may o course be added. Using fresh acid, 100 pounds of toluene and about 250 pounds of -38 per cent. nitric acid may be employed. "About 0.10

ct cent. paraformaldehyde may be added, t 4 e additions being in small portions from time to time. With acid stronger than about 43 per cent., there is too much side, reaction in the way of nitration, that is, production of nitrocompounds and the like, while with acids much weaker than 35 er cent., the action is entirely too slow. acid as weak as 20 per cent., it is almost im possible to start the action. As toluene boils at 110 C., it is usually inconvenient, unless unusually eflicient refluxing means or pressure be employed, to operate much above, say, 105 C. A temporature of 95 to 98 C. in working under the usual pressure with the usual condensing means is convenient. '-In working under ressure, somewhat higher temperatures may employed with consequent quickening of ,4

they may be of different the operation. The extra pressure when employed should' be air pressure, air being forced into the apparatus by a suitable ump. This gives a greater body of oxygen or regenerating the nitrous fumes. A great economy in acid may be-efi'ected by introducing intothe apparatus a body of oxygen itself under pressure. However, a very sub stantial degree of-oxidation with much economy of acid is efl'ected'by working at the ordlnary pressure in an apparatus having an air space several times the vo1umeoccupied bythe liquids. Temporary fluctuations 1n pressure due to fluctuations in temperature will provide fresh air in the apparatus as fast as the oxygen is used up by the acid.

After the completion of the oxidation the materials are cooled and the s ent acid re. moved from the solid crystal ine crust of benzoic acid and admixed oil (a mixture of unchanged toluene, benzaldehyde, etc), and

returned for use in diluting strong nitric acid. As stated, the strength of th s nitric acid is froml? to 18 er cent. of real acid and asmall addition 0 ordinary commercial acid suflices to bring it up to the preferred 38 per cent. A mixture of spent acid which contains some dissolved'organic bodies with fresh acid starts reaction much more quickly thanfresh acid diluted with water. The crystalline crust is next treated to convert the benz oic acid into benzoate of soda. For this purpose, it istaken up by a solution of sodium carbonate (soda ash) or caustic soda, as convenience may dictate. An oily layer of toluene, benzaldehyde, etc., which sepa-' rates from the aqueous lever is returned for admixture with fresh toluene.

' It will be noted that in the present method there is no substantial waste, either of acid or of toluene. The conversion of the toluing, quantitative, while the acid, as stated,

-ene into benzoic acid is, practically speakfunctions to an extent somewhat more than its calculated oxidizing power by reason of the regeneration mentioned. either material as occur are mostly mechanical.

Operating in the manner described,

losses-due to nitration are very small. Such nitration as occurs under the prescribed conditions is mostly in the side-chain.

The solution of sodium benzoate may 'contain nitrocompounds which may be removed by treatment with a reducing agent, such as sodium acid sulfite, crude calcium sulfid (liver of sulfur), tin and hydrochloric acid, etc. By this reduction the nitrocompounds are converted into amino compounds which are readily removed. It may then be acidulated and benzoic acid recovered in the usual way. Sulfuric acid, niter cake (sodium hydrogen sulfate), etc., may be employed for acidulation. Hydrochloric acid may be employed but in its presence greater care is nry in order to obtain a ChlOl'ill-fl'flfi Such losses of final product. However, the sodium chlorid--- thou h at times it contains organic bodies whic may yellow the product a little. In using this nitric acid, therefore, as in the case of using hydrochloric acid, good wash: ing must be resorted to. The benzoic acid reco ered may be'purified by sublimation, crystallization, etc., in the usual ways. The benzoicacid produced of course contains no chlorinated compounds.

Instead of forming benzoic acid from the solution of sodium benzoate in the'mann'er descrlbed, sodium benzoate itself may-be recovered from the solution in-an-y appropriate waiy and marketed as such.

stead of formingsodium.benz-oate from' the crude benzoic acid produced in the described process, calcium 'benzoate in. be ialk,

. produced by the use of milk'oflime, 2

etc. Or, the material may be simply treated with enough soda, lime, chalk, etc.,' to ne u' tralize the nitric acid' present and the benzoic acid recovered and purified in any suitable way.

.While the present invention has been described more articularlyin its application to the manu acture of 'benzoic acid from toluene, it may of course be applied to other .side-..c-hain derivatives ofbenzene (benzol),- such, as ethylbenzene; and" it may be apliedfto the manufacture of other acids than enzoic acid. For example, orthomtrotol- 4o-1 1ene on oxidation with nitric acid in an analogous manner. gives orthonitrobenzoic acid fromwhich. by reduction, anthranilic toluene with hot nitric acid of about per acid- (or -orthoaminobenzoic acid) may be obtained; the latter being a valuable mate rial in theindigo synthesis. In addition, the same type of reaction may be utilized for the preparation of valuable local anes thet-ics of the amino benzoic series. 'Witlr this material as with others boiling at higher temperaturesthan toluene somewhat higher temperatures may be employed 1n the oxidation, with consequentacceleratmn of the process. 'With materials of greater specific gravity than that ofthe nitric acid used in order to obtain the desired stratification an expedient may be used. this. expedient consisting in dissolving S0tllll1l1 nitrate 1n the acid. By oxidizingone of the x vlols in a similar manner to that above indicated tolmacidnnay be obtained andithis, upon further oxidation, is converted into the corresponding phthalic acid. The process is not applicableto the phenols, such as cresol,

unless the phenol group be protected by esterificationj in which event from orthocresol salicylic acid is obtained.

' 'hat we claim is 1. The process of oxidizing organic aromatic bOdlGS having side-chains with nitric acld'to' produce acids, which comprises stratifying such organic bodies with nitric acid of 1 strength between 20 and 43 per cent. H) 0 and maintaining the two in contact at a high temperature until reaction is complete.

2. The process'of oxidizing organic aromatic bodles having side-chains with nitric acid to produceac'ids which comprises stratifying such organic bodies with nitric acid of about 40 per cent. strength and maintainingthetwo-in contact at ahigh temperature until reaction is complete.

3. The process of making benzoic acid from toluene which comprises stratifying "toluene with between 20 and 43 per cent.

HXO, nitric acid at a temperature somewhat below the boiling point of toluene and allowing the acid and toluene to remain in contact until the reaction is substantially complete.

4. The process of making benzoic acid from toluene which comprises stratifying toluene with between 20 and 43 per cent. HXO, nitric acid at a temperature somewhat below the boiling point of toluene-and allowing the-acid and toluene to remain in contact .until the reaction is substantially complete,

escaping vapors being condensed and returned to the materials undergoing reaction.

5. The 'processof making benzoic acid.

from toluene which comprises stratifying cent. strength containing a little reducing agent and allowing the two to remain in contact hot until the reaction is substantially complete. a

6.' The process of making benzoic acid from toluene which comprises stratifying toluene withhot nitric acid of about 0 per cent. strength containing [a little formaldehvde and allowing the two to remain in contact hot until the reactionis substantially complete.

In testimony whereof we aflix our signatures hereto.

"I'RGIL COBLEXTZ. HAROLD V. VALKER. 

